After re-installing iTunes 11.0.2 it may show an error message reading one of iTunes' ".itl" files. Ideally, you will be able to replace this file with an older version that you have previously backed up using Time Machine. Failing that, the solution is to re-import your music after telling iTunes not to organize and not to copy files (don't forget to re-set the organize/copy settings back to what they were afterwards).